Television receiver



Se'pt. 19, 1939.

H. M.l I Ewls TELEVISION RECEIVER Filed Dec. 10,v 1936 Patented Sept.19, 1939 UNITED Is'rATI-:s

2,173,173 j TELEVISION RECEIVER Harold M. Lewis, Great Neck, N. Y.,assignor to Haseltine Corporation, a corporation of Deia- WINApplicationl December A'10, 1936, Serial No.`1l5,068v

Claims.

This invention relates to program receivers for use in carrier-frequencyprogram broadcasting systems and in particular invsystems, such asytelevision systems, in which each station trans- 6 mits a plurality ofcomponents of a uniiled program on separate but related carrier waves,one component, for example the vision component.

being transmitted as a broad band of modulation frequencies, and theother component, such as a l0 sound component, being transmitted as arelatively narrow band of modulation frequencies.

In the transmission of television programs by radio broadcast, it hasbeen proposed that each` program should comprise a broad band oimodulation frequencies of the lorder of three megacycles representingthe vision component and centered about itscarrier frequency and anarrow vband of modulation frequencies of the order of one-quartermegacycle or less representing the sound component and centered about acarrier frequency adjacent that of the vision component and spaced onlysuiilciently to avoid interference between the two signal components.The exacting requirements for accurate definition of the televisionimage, leading to the use of such an extremely wide band ofmodulation*-frequencies,` increases the diiliculties in the design ofthe selecting, amplifying, and transmitting circuits of thevision-signal channel of the receiver. Thereso fore, these circuits aredesigned to transmit uni-v formly a frequency band as wide, but only aswide, as is necessary to obtain reasonably -accurate deflnition of thetelevision image and it is important that the vision-signal channel ofthe receiver shall be tunedv as accurately as possible to avoid cuttingor attenuating any of the sideband frequencies essential for an accuratereproduction of the image. On the other hand, since thesignal-selecting-circuits ofthe vision-signal 40 channel pass a wideband of frequencies, there is little or no variation in the intensity ofthe carrier frequency output of the selector for mistuning of the visionchannel -of the receiver up to atleast a one-half of the band width.Since the intensity of the carrier-frequency output of (Cl. P18-7.5)

vision signal is transmitted through the soundsignal channel, resultingin harsh noises, `while a sound signal is transmitted through thevision-- signal channel, resulting in objectionable flashes of. lighton, or damage to, the screen of the `vision- 5 f signal 'reproducen Itis anv object of the invention, therefore, to provide an improvedprogram receiver for use in Va carrier-frequency program broadcastingsystem in which a first component of each-pro- 10 gram is transmitted asa broad band ,of modulation frequencies on one carrier wave and a secondcomponent is transmitted as a narrow band of modulation frequencies on arelated carrier wave, including means for accurately indicating l5 thecorrect tuning of the receiver, that is, the

condition in which the broad-band signal compo- `when the broad-bandsignal component is accu- 25 rately centered with respect to itsbroad-band se- .n lector.

It is a further object of the'inventicn to provide an improved programreceiver, for use in a system of the type described, in which' the nar-80 row-band signal channel is maintained in an inoperativefconditionexcept when a signal having a predetermined component characteristic ofthe desiredl broad-band signal is received by the broad-band signalchannel.

In accordance withlthe invention, an improved program receiver, for usein a system of the typeI described, comprises a. `nrstsignal-translating channel including a broad-band selector for a iirstprogram component and a first signal-reproduc- 40 ing means coupledthereto; a second signal-translating channel including a narrow-bandselector for. the second program component and a second ysignal-reproducing means coupled thereto. The

receiver includes also means responsive silelyv tol the signal output ofthe narrow-band selector for f controlling the signal-transmissioneiiiciency ofA the signal channel for the broad-band program' componentand means for maintaining said narrow-band signal channel in rativeexcept-when a signal having a predetermined characteristic' nel. Y l

In a preferred embodiment of the invention, for

use ina television broadcasting system in which 56 is being'received bythe broad-band signal chanl the vision signal component includes acharacteri'stic component such as a synchronizing-signal component orother periodically recurrent modulation-signal component and in whichthe sound-signal component comprises only non-recurrent signalcomponents, the broad-band signal-reproducing means comprises acathode-ray tube including one or more control electrodes normallybiased to suppress the cathode ray. Coupled to the output of thenarrow-band selector is the sound-reproducing means and means forderiving a bias voltage proportional to the amplitude of thecarrierrequencycutput of the narrow-band selector, the range ofproportionality being limited by a tube operating beyond its upper andlower saturation points for signals above a predetermined value, andimpressing it positively upon an electrode o1" the cathode-ray tube toinitiate a ray therein. By means of this arrangement, the vision-signalchannel is normally maintained inoperative until the sound-signalchannel has been accurately tuned, as evidenced by the developing of abias voltage of suicient value to initiate and maintain the cathode ray.By virtue of the relatively extreme selectivity of the narrow-bandselector, whenever the receiver is tuned suiliciently accurately tcobtain a substantial signal output from the narrow-band selector, itwill be tuned to center the vision signal with respect to the broad-bandselector with suincient accuracy to ensure the transmission of theessential modulation frequencies for an accurate reproduction of theimage, so that an indication of the proper tuning of the receiver' isgiven in accordance with the illumination of the cathoderay tube.

In order to ensure that the receiver will be maintained inoperativeexcept when each signal channel is receiving its characteristic type ofsignal, there is coupled to the output of the broadband selector, meansfor deriving a bias voltage dependent upon a predeterminedcharacteristic thereof, such as the synchronizing impulses of a visionsignal or other periodically recurrent modulation-signal component. Thisbias is impressed y positively on an electrode of a tube of thesoundsignal channel preceding the point from which the mst-mentionedbias is developed, thereby overcoming a normal negative bias suppliedsuch electrode and rendering the channel operative.

It is understood that the term carrier frequency, as used herein, referseither to a radio frequency or an intermediate frequency and that theselectors of the receiver may operate at either radio frequencies orintermediate frequencies in accordance with whether the receiver is ofthe tuned radio frequency or superheterodyne type.

Also, the expression tuning of the receiver as used herein refers to theadjustment of the resonant frequencies of the radio-frequency selectors'or the local oscillator, or both.

For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

In the drawing, Fig. i is a schematic diagram of a complete televisionreceiving system embodying the invention',v while Fig. 2 is a chartillustrating the relation between the program components in a televisionsystem oi the type which the system of Fig. 1 is designed to receive.

Referring now more particularly to Fig. l of the drawing, there isillustrated, partially schematically, a complete television receiver ofthe superheterodyne type embodying the invention and including anantenna circuit II coupled to a radio-frequency amplier I2, which isconnected, in cascade, with an oscillator-modulator' I3, avideo-intermediate-frequency amplifier and selector Ili, avideo-frequency detector I5, a video` frequency amplifier and selectorId, as indicated. II, constituting the vision-signal channel of thereceiver. An automatic amplication or contrast control (A. C. C.) may beconnected from the output of the detector I5 to the control electrodesof one or more of the tubes of the intermediatefrequency amplifier andselector Id, as indicated. The elements described may be of conventionalconstruction, so that a detailed illustration and description isconsidered unnecessary herein.

The cathode-ray tube II comprises the usual envelope I8 containing anelectron gun comprising a cathode heater I9, a cathode 20, a main orvideo control grid 2|, an accelerating anode 22 for generating andaccelerating an electron stream, and a focusing anode 23 for focusing itinto a beam. The envelope is also provided with a second anode 24usually comprising a conductive coating on the interior surface and theusual fluorescent screen 25 formed on the end oi' the tube.Line-frequency and frame-frequency scanning or deflectingicoils 27 and2G, respectively, are disposed about the neck of the tube I'I fordeveloping a eld normal to the axis of the tube, for deecting thecathode ray.

The video-frequency amplifier i6 is coupled to the control grid 2|' ofthe tube Il by meansof a coupling condenser 28, a blocking resistor 29.and a by-pass condenser 3|, while the scanning coils 2l' and 26 areenergized from the line-frequency generator 33 and frame-frequencygenerator 32, respectively, also coupled to the video-frequencyamplifier to receive therefrom synchronizing lmpulses transmitted withthe video signal, thus synchronizing the scanning of the cathode-raytube with the scanning of the image at the transmitting station. Forsupplying operating potentials to the various electrodes oi' the tube I1, there is provided a voltage divider 34 adapted for connection to asuitable direct current source (not shown) and having a tap 84a forsupplyinga bias to the control grid 2| through an isolating resistor 35and taps 34h, 34o, and 34d connected to the anodes 22, 23, and 24,respectively. Certain of these'taps may be manually adjustable forregulating the initial bias voltages applied to the tube electrodes andfor controlling the operation of the system.

The sound-signal channel comprises the antenna circuit II. theradio-frequency amplifier I2, and the oscillator-modulator Il in commonwith the vision-signal channel and, coupled thereto in cascade, lanaudio-intermediate-frequency amplifier and selector fan audio-frequencydetector 31, an audio-frequency amplier 38, and a sound `reproducer 3,9.An automatic amplification or volume control..(A.vV. CJ may be oonnectedfrom the output of the detector 81' to the control electrodes of one ormore of' the tubes of the intermediate-frequency amplier and selector36, as shown.-

The systemof Fig. 1, as thus far described, is

conventional in construction and operation so by. the antenna circuit IIare selected and amplided in the radio-frequency ampliiier'iz and sup-Signals are converted Iinto intermediate frequen The intermediatecies inthe usual manner. frequency amplier and selector I4 Aselectively .iamplifes the vision-modulated intermediate-fre Vquency carrier andsupplies it to the detector I5 where the video-frequencies of modulationare derived and subsequently amplified by the ampli. er I6 and suppliedin the conventional manner :to the control grid 2I of the cathode-raytube I1 and to the scanning generators 32 and 33. With proper operatingpotentials supplied to the electrodes of the tube I1, a stream ofelectrons is generated, accelerated, and focused`by the electron guncomprising the elements I9, 20, 2|, 22,

and 23, which strikes the fluorescent screen 25 of the tube. Theline-frequency and frame-frequency generators 33 and 32,-respectively,generate periodic currents of saw-tooth Wave form y synchronized withthe Scanning circuits of the transmitter and supply them to thedeflecting coils 21 and 2 6. The magnetic fields produced by the coils26 and 21 of saw-tooth wave form are eiectiveto cause the cathode ray toscan the screen 25 rectilinearly to reproduce the' trans-Y mitted image.

Simultaneously, the amplier and selector 36 selectively ampliiies thesound-modulated intermediate-frequency car- Y yrier and transmits it tothe detector 31 where the audio frequencies of modulation are derivedand subsequently amplied in the amplifier 38 and reproduced by theloud-speaker 39.

In order to ensure that-the vision-modulated l: carrier is accurately`centered with respect tothe intermediate-frequency selector and amplierI4', there is provided an arrangement for4 controlling the operation ofthe cathode-ray tube I1 in accordance with the accuracy of tuning of thesound-signal channel, the selector of which, as stated above, passes aband which is extremely narrow relative to that of the vision-signalchannel. The arrangement includes a vacuum-tube repeater 40 coupled tothe output of the linterij mediate-frequency amplifier 36 byv means of acoupling condenser 4I and a grid leak 42. The

`output circuit of the repeater 40 is coupled by means of anintermediate-frequency selector 43 to ay diode vrectifier 44. Theselector 43 has a selectivity of the same order as, or sharper than,lthat of the selector36.- Suitable operating potentials are provided forthe tube 40, as indicated by +Sc and +B. The rectifier* 44 is providedwith a' load circuit comprising a resistor 45 by,

passed by a condenser46,. while its cathode is' effectively grounded forintermediate frequencies by condenser 41. The load resistor 45 of therec- Y tier '44 is included in series in 'the connection allysuppresses, the cathode ray of the tube I1,

so that the screen 25 is not illuminated. When the receiver isaccurately tuned, that-is, when the sound-modulated carrier isapproximately centered with respect to the selector and a signal isbeingV received, th signal outpptLof the selector 36 is of substantialamplitudesapd, a. `substantial intermediate-frequency chronizingcomponent.

bias voltage is developed across the resistor 45 which is superimposedupon that supplied by the tap 34D, the sum of the two voltages being ofsuflicient magnitude to initiate and maintain the cathode ray in thetube I1 to reproduce the transmitted image in the conventional manner.In order to minimize the effect of normal variations in the signaloutput of the selector 36, due either to an inexact tuning of thesound-signal channel lor to variations in the strength of the signalinput, the characteristics of the repeater 40 are so selected withreference to the magnitude of its -input voltage and its circuitconstants that it becomes saturated for .signal inputs of apredetermined value somewhat less than the normal signal output of theselector 36. With such an arrangement, the bias voltage developed by therectifier 44, for values of signal output of the selector 36substantially less than normal, is proportional to the signal-input torepeater 40 but is insuicient to initiate the cathode ray in the tubeI1, while increases in the signal output of the selector 36substantially beyond this normal value do not effect appreciableincreases inthe bias voltage developed by the rectifier 44, which mightaffect the intensity of the cathode-ray beam and thus the averagebackground illumination of the reproduced'image.

In order to prevent the occurrence of clisturbing light ashes on, ordamage to, the screen of the cathode-ray tube I1 uponl thel reception ofsignals other than television signals and the vision-signal channel,there is providedan arrangement for maintaining the sound signal channelinoperative except when a signal having a component characteristic of a.television signal is received bythe vision-signal channel. arrangementincludes a vacuum-tube repeater 50 coupled to the output of thevideo-frequency amplifier I6 by means'of a coupling condenser 5I and agrid leak 52. The output circuit of the repeater 50 is coupled to adiode rectler 54 by means of a selector 53 sharply` tuned to one of thecharacteristic modulation components of a television signal, preferably,a periodically recurrent signal component such as the line-frequencysyn-I tentials are provided for the tube 56, as indicated by -I-Scand+B. `The rectifier 54 is provided with a load circuit comprising aresistor 55 bypassed by a condenser 56. A control circuit is providedfor one or more of the tubes of the audio-intermediate-frequencylamplifier 36, including a source of negative-bias potential 51 and theload resistor 55 ofthe rectifier 54 connected with such polarity as to'oppose the bias source 51.

In the operation of the last described control amplier 36 is normallybiased to an inoperative condition'by the battery 51 which action, inturn,

This

Suitable operating po- .arrangement, the audio-intermediate-freouencyremoves the signal input to the auxiliary control A age, for normal-received signals, being sufficient to overcome the negative -bias ofthezbattery 51 and render conductive the tube or tubes of thevaudio-intermediate-frequency amplifier 36. In

order to minimize the eect of the normal varla- I as a narrow band ofmodulation frequencies on tions in the amplitude of the predeterminedsignal component in the output of the video-frequency amplifier i6, dueto variations in the strength of the signal input or other causes, the

characteristics of the repeater tube 50 are so selected with referenceto the magnitude of its/ inputI voltage and its circuit constants thatit becomes saturated for signal inputs of a predetermined value somewhatless than the normal amplitude of the predetermined component of thesignal output of the amplifier i6. With such -an arrangement, the biasvoltage developd by the rectifier 54 for all values of signal outputofthe amplifier I5 substantially less than normal is inj sufficient toovercome the bias 5'! and render the sound-signal channel operative,while increases in the signal output of the amplifier I6 substantiallybeyond this normal value do not eiect appreciable increases in the biasvoltage developed by the rectifier 54, which might ailect thetransmission eiliciency of the sound-signal channel and, thus, thelevelof the sound output thereof. Fig. 2 is a chart of the relation betweenthe vision modulation band, the sound modulation band and theradio-frequency or intermediatefrequency carriers as it has beenproposed to relate them for each television-broadcast station. It willbe noted that the vision modulation band a is a. band approximately 5megacycles in width centered about a carrier frequency lv, which isspaced by 2-.75 megacycles from one edge of the allotted signal channel,while the sound modulation band b comprises an extremely narrow bandcentered about a carrier frequency at the other edge of the signalchannel. The band b may be extremely narrow` and still provide adequateAtransmission of the sound modulation frequencies. As a maximum widththis band may be of the order oi" 0.25 megacycle in order to allow forreasonable drift of the local oscillator or the carrier frequency. Thus,whenever the receiver is tuned suiliciently accurately that thesoundsignal is even approximately centered with respect to the pass band ofthe selector 16 so as to produce a substantial control voltage on theaccelerating anode 22 of the tube i1, the vision modulation band mustnecessarily be centered with respect to the pass band ofthe selector i4with such accuracyas to transmit and reproduce the essential modulationfrequencies for an ,accurate reproduction of the transmitted scene.There is thus given an indication of the proper tuning of Vthe receiverin accordance with the illumination of the cathode-ray tube I1. At thesame time,

the entire receiver is rendered inoperative except modications as fallwithin'the true spirit andV scope of the invention.

What is claimed is:

1. In a carrier-frequency Program broadcasting system in which a rstcomponent of each program is transmitted 'as a broad band of modulationfrequencies on one carrier Wave and a second component of each programis transmitted another carrier wave related in frequency to said rstcarrier wave, a program receiver comprising a rst signal-translatingchannel including a broad-band selector for said rst program componentand a cathode-ray signal-reproducing tube coupled thereto, saidcathode-ray tube having a control electrode normally biased to suppressthe cathode ray, a second signal-translating channel including anarrow-band selector for said second program component and a secondsignal-reproducing means coupled thereto, and means for giving anindication oi the tuning of the receiver in accordance with theillumination of said cathode-ray tube comprising a repeater tube coupledto the output circuit of said narrow-band selector, said tube being sodesigned relative to the constants of its associated circuit that itsaturates for input voltages above a predetermined value. rectliiermeans coupled to said repeater tube for deriving a bias voltageproportional to the input' to said repeater tube for inputs below saidpredetermined value, and means for impressing said bias voltagepositively on said control electrode to initiate and maintain thecathode ray only when the signal input to said repeater approximatessaid predetermined value.

2,. In a carrier-frequency television broadcasting system in which thevision-signal component of each program is transmitted as a broad bandof modulation frequencies on one carrier wave and the sound-signalcomponent of each program is transmitted as a narrow band of modulationfrequencies on another carrier wave related in frequency to said rstcarrier wave, a program receiver comprising a first signal-translatingchannel including a broad-band selector for said vision-signal componentand a cathode-ray signal-reproducing tube coupled thereto and providedwith a control electrode normally biased to suppress the cathode ray, asecond signal-translating channel including a narrow-band selector, iorsaid sound-signal component and a loudspeaker coupled thereto. andcontrol means coupled to, and responsive solely to, the signal output ofsaid narrow-band selector for modifying the bias of said controlelectrode to initiate and maintain the cathode ray, said control meansincluding means for limiting the controlling eifect on said controlelectrode to a substantially constant value for outputs of saidnarrow-band selector above a predetermined value, whereby theillumination of said cathode ray tube affords an indication of thetuning' oi said sound-signal channel and is unaffected by said controlmeans during normal operation.

3. In a carrier-frequency pro broadcasting system in which a firstcompon nt of each program is transmitted as a broad bandpf modulationfrequencies on one carrier wave and a second component ofeach program istransmitted as a narrow band of modulation frequencies on anothercarrier wave related in frequency to said rst carrier wave, a programreceiver comprising a rst signal-translating channel including abroad-band selector for said first program component and a rstsignal-reproduclngmeans coupled thereto. a second signal-,translatingchannel including a narrow-band selector for said second programcomponent and a second signal-re'" producing means coupled thereto:means responband selector for controlling the signal transmissionefficiency of said rst signal channel, and.

means responsive to the reception by said first signal-translatingchannel of a signal having a predetermined characteristic component forcontrolling the transmission efficiency of said secondsignal-translating channel vat a point preceding the output of saidnarrow-band selector.

4. In a carrier-frequency program broadcasting system in which a firstcomponent of each pro'- gram istransmitted asa broad band of modulationfrequencies on one carrier wave and a second component of cach programis transmitted asl a narrow band of modulation frequencies on anothercarrier wave related in frequency to said first carrierwave, a programreceiver comprising a first signal-translating channel including abroad-band selector for said first program component and a rstsignal-reproducing means coupled thereto, a second signal-translatingchannel including a narrow-band selector for said second programcomponent and al second signalreproducing meansv coupled thereto, meansresponsive solely to the signal output of said narrow-band selector forpreventing `operation of said rst signal-reproducing means whenever saidsignal output is less than a predetermined magnitude, means forbiasingfsaid second signal-translating channel to an inoperativecondition, and means responsive to the reception by said firstsignal-translating channel of a signal having a predeterminedcharacteristic component for overcoming said biasing means to rendersaid second signal-translating channel operative.

ing system i'n which a` first component of each program is transmittedas a b road band of modulation frequencies on one carrier wave and aseccoupled thereto,

ond component of each program is transmitted as a' narrow band ofmodulation frequencies on row-band selector for controlling the signaltransl mission efficiency of said first signal channel, control meanscoupled to the output of said broad-band selector and including a.selector sharply responsive at the frequency of a predeterminedcharacteristic component of a desired broad-band'signal, and meansresponsive to the output of said last-named selector for` controllingthe transmission efficiency of said second signaltranslating channel ata point preceding the output of said narrow-band selector.

6. In a carrier-frequency program broadcast-l ing system in which afirst component of each program is transmitted as a broad band ofmodulatiorr frequencies on one carrier wave and a second component ofeach program is transmitted as a narrow band'of modllation frequencieson 'another carrier'wave related in frequency to said first c arrierwave, a program receiver comprising a first signal-translating channelincluding a broad-band selector for said flrst program cornponent and afirst signal-reproducing means a second signal-translatingchannelincluding -a narrow-band selector for said ,second programcomponent and a second signal- 5. In a carrier-frequency programbroadcast--A reproducing means coupled thereto, means responsive solelyto the signal output of said n arrow-band selector for controlling thesignal trans-l mission eiilciency of said first signal channel, arepeater tube coupled to theloutput circuit of said broad-bands'elector, said tube being so designed relative to the constants of itsassociated circuit that it satur'atcs for input voltages a'bove apredetermined value, a selector circuit coupled to the output of saidrepeater tube and sharply responsive at the frequency of a predeterminedchai'- acteristic4 component of a desired broad-bard v signal, rectifiermeans Afor deriving from the outsignal input to said repeaterapproximates s aid predetermined value. y 2o '7. In a carrier-frequencytelevision broadcastling system in .which the vision-signal component ofeach program is transmitted as a broad band of modulation frequencies onone carrier i wave and the sound-signal component of each program istransmitted as a narrow band of modulation frequencies on anothercarrier wave related in frequency to said first carrier wave, a programreceiver comprising a first signal-translating channel including abroad-band selector 30 for said vision-signal component and a cathoderaysignal-reproducing tube coupled thereto and provided with a controlelectrode normally biased to suppress theA cathode ray, a secondsignaltranslating channel including a narrow band selector for saidsound-signal component and a loud-speaker coupled thereto, meansresponsive solely to the signal output of said narrow-band j selectorfor modifying'thebias of said control electrode to initiate and maintainthe cathode ray when said signal output exceeds a predeter- 'minedvalue, whereby the illumination of said vcathode ray affords anindication of the tuning of said sound signal channel, means for biasingsaid second signal-translating channel to an inop- 45 erative conditionat a point preceding the output of said narrow-band selector, and meansresponsive to the reception by said first signal-translating channel .ofa vision signal including a synchronizing-frequency component forovercoming said biasing means to restore said `second signaltranslatingchannel to normal operating condition.

i 8. In av carrier-frequency program broadcasting system in which eachof a pair of components 55 of each program is transmitted as a band ofmodulation frequencies on a carrier wave having a predeterminedfrequency relation to the carrier wave of the other component of thesame program, one of said program components having a characteristicmodulation component, a program receiver comprising a pair of signalchannels, each of said [channels including signalselecting, y-amplifyingand -detecting means and a signal-translating device coupled thereto,the 65 signal-selecting means of said channels' being individuallyresponsive to frequencies having said vpredetermined relation to eachother, and means for determining the allocation of each programcomponent to its proper channel comprising 70 means selectivelyresponsive to said characteristic modulation component coupled to itscorresponding signal channel for controlling the signal-transmissionefficiency ofthe other signal channel, and means responsive to' thesignal ampli'tude at a point in said other signal channel subsequent tothe point at which it is controlled for controlling thesignaltransmission efficiency of said first-named signal channel at apoint subsequent to the point to which said selectively responsive meansis coupled.

9. nra carrier-frequency program broadcasting system in whicha firstcomponent of each program is transmitted as a carrier Wave modulatedwith a recurrent periodic signal component and a second component oieach program is transmitted as a carrier Wave modulated with anon-recurrent signal component and having a predetermined frequencyrelation to said firstnamed carrier, a program receiverr comprising apair of signal channels, each of said channels includingsignal-selecting, -amplifyingand detecting means and asignal-transmitting device coupled thereto, th signal-selecting means ofsaid channels being individually responsive to frequencies having saidpredetermined relation to each other, and means for determining theallocation of each program component to its proper channel comprisingmeans selectively responsive to said recurrent signal component coupledto its corresponding signal channel for controlling thesignal-transmission eiiiciency of the other signal channel, and means4responsive to theY signal amplitude at a point in said other signalchannel subsequent to the point at which it is controlled forcontrolling the'signal-transmission eilciency of said first-named signalchannel at a point subsequent to the point to which said selectivelyresponsive means is coupled.

10. In a carrier-frequency program broadcasting system in which a rstcomponent of each program is transmitted as a carrier wave modulatedwith a recurrent periodic signal component and a second component ofeach program is transmitted as a carrier wave modulated with anon-recurrent signal component and having a predetermined frequencyrelation to said firstnamed carrier, a program receiver comprising apair of signal channels, each of-said channels includingsignal-selecting, -amplifying and-detecting means and asignal-translating device coupled thereto,- the signal-selecting meansof said channels being individually responsive to frequencies havingsaid predetermined relation to each other, means for normally biasing tocut oi a portion of the signal channel for said rst pro gram componentsubsequent to its detecting means, means for normally biasing to cut o aportion of the other signaltchannel, and means for determining theallocation of each program component to its proper channel comprisingmeans for deriving from the detecting means of said first-named channella bias voltage dependent upon said recurrent signal component andapplying it to overcome the cut-off bias of the other signal channel,and means for deriving from said other signal channel a bias voltagedependent upon the signal amplitude therein subsequent to the biasedportion and applying it to overcome the bias o! said first-namedchannel.

HAROLD M. LEWIS.

